In Vondrousova's five previous matches against Top 10 opposition, the 19-year-old had forced a decider on four occasions - but had yet to emerge with a win. Today, she changed that in impressive fashion, showcasing both power and finesse en route to her maiden Premier quarterfinal.

In conjunction with 18-year-old Bianca Andreescu's earlier upset of No.18 seed Wang Qiang, the result means that two teenagers will play the Indian Wells quarterfinals for the first time since 2009, when Caroline Wozniacki, Victoria Azarenka?and Anastasia Pavlyuchenkova all made it to the last eight. Halep's loss also ensures that Naomi Osaka will remain World No.1 after the tournament.

Despite a patchy opening sequence of five consecutive breaks of serve, Vondrousova's all-court proficiency was nonetheless made clear. The Czech fired a wickedly angled return winner and a heavy cross-court forehand to break immediately, and would demonstrate a cool-headed strategy to penetrate Halep's elite defence. Able to create remarkable angles off both wings and vary her balance between aggression and counterpunching, it was the Roland Garros champion who found herself goaded into error more often than not.

Vondrousova, who reached the fourth round in Indian Wells last year, would also find success with a number of delectable dropshots which were too much even for Halep's renowned foot speed - and once the Budapest finalist was able to notch up her first service hold in the sixth game, she drew away, breaking Halep for a fourth time with a drive volley and sealing the set with a one-two punch.

Having won a mere seven points on serve in the opening stanza, an improvement in this area was a key priority for Halep - and the 27-year-old turned it around brilliantly in the second set. She had won only 29% of her first serve points in the first set, and while greater aggression on the shot saw a fall in her first serve percentage from 74% to 48%, the pay-off was in its efficacy: Halep did not concede a point behind her first delivery in the second set, and only dropped three service points in total.

Meanwhile, Vondrousova's shot selection was slipping: having fallen behind a break for 1-3 with her first double fault, she would back off on a number of key rallies, in particular an exhausting exchange in the fifth game in which she repeatedly hit short balls back to Halep rather than the open court, and eventually made the mistake.

Entering the decider, Halep seemed in full flow, even beginning to track down two Vondrousova dropshots to capture the point - aided by her opponent's failure to anticipate her chases and counterdrops - and eventually the opening break.

But instead, just as Vondrousova seemed to have run out of ideas and energy, it was the 2017 Biel champion who essayed a remarkable turnaround. Consecutive double faults from Halep handed the break back immediately; at 30-30 in the third game, Vondrousova managed to redirect a remarkable angle cross-court at full stretch, and then power a forehand winner after a high-intensity rally to move up 2-1.

Racing to a 5-1 lead, the left-hander's forehand down the line would come through in a major way just when she needed it; by contrast, a cascade of errors would flow from the Halep racquet, particularly off her backhand wing, eventually reaching a total of 36 to only six winners.

Although Vondrousova was unable to close the biggest win of her career out on her own serve, a break to love courtesy of four such backhand mistakes from Halep sealed the match in the next game. Up next in the last eight will be either No.6 seed Elina Svitolina or No.12 seed Ashleigh Barty.